For DSL technologies that support multiple sub-channels on one line, when the multiple sub-channels are indeed used at same time, this parameter indicates which sub-channel will be used for this QOS profile. When only one sub-channel is used this parameter has no effect... EXAMPLE: in DMT - when the latency is set to BOTH, sub-channel #1 is the FAST channel ( typically useful for voice traffic - voice over ATM or Packet ) while sub-channel #2 is the INTERLEAVE channel ( typically useful for data traffic ).